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(#) Trusting ContentProvider filenames without any sanitization

!!! WARNING: Trusting ContentProvider filenames without any sanitization
   This is a warning.

Id
:   `UnsanitizedFilenameFromContentProvider`
Summary
:   Trusting ContentProvider filenames without any sanitization
Severity
:   Warning
Category
:   Security
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   8.8.0 (January 2025)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
See
:   https://developer.android.com/privacy-and-security/risks/untrustworthy-contentprovider-provided-filename
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/UnsafeFilenameDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UnsafeFilenameDetectorTest.kt)

  When communicating between applications with files, the server app can
provide the client app with a maliciously constructed filename. The
client app should never trust this filename and should either sanitize
it or completely discard it.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/TestClass.java:10:Warning: Using fileName is unsafe as it is a
filename obtained directly from a ContentProvider. You should sanitize
it before using it for creating a File.
[UnsanitizedFilenameFromContentProvider]
    File fileObject = new File("./", fileName);
                                     --------
src/TestClass.kt:10:Warning: Using fileName is unsafe as it is a
filename obtained directly from a ContentProvider. You should sanitize
it before using it for creating a File.
[UnsanitizedFilenameFromContentProvider]
    val fileObject = File("./", fileName)
                                --------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`src/TestClass.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
import android.database.Cursor;
import android.provider.OpenableColumns;
import java.io.File;

class TestClass {
  private void trustProvidedFilename_shouldWarn(Cursor cursor) {
    int id = cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
    String fileName = cursor.getString(id);

    File fileObject = new File("./", fileName);
  }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/TestClass.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
import android.database.Cursor
import android.provider.OpenableColumns
import java.io.File

class TestClass {
  private fun trustProvidedFilename_shouldWarn(cursor: Cursor) {
    val id = cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME)
    val fileName = cursor.getString(id)

    val fileObject = File("./", fileName)
  }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UnsafeFilenameDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("UnsanitizedFilenameFromContentProvider")
  fun method() {
     getColumnIndex(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("UnsanitizedFilenameFromContentProvider")
  void method() {
     getColumnIndex(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection UnsanitizedFilenameFromContentProvider
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="UnsanitizedFilenameFromContentProvider" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'UnsanitizedFilenameFromContentProvider'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore UnsanitizedFilenameFromContentProvider ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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